The invention relates to a chair of the type which allows movement of its backrest and seat.
Typically, chairs have been designed with functional details of the chair parts and the mechanism in mind rather than response to health or supportive movement of the occupant. While this approach tends to provide a chair which is reasonably reliable and conforms to safety standards, the chair is typically not particularly comfortable and supportive. Also, this approach does little to reduce the risk of repetitive strain injury (RSI) caused by a mainly static support system.
European Patent Specification No. 22933 (Grammer) describes a chair having a seat and a backrest which are set to positions to provide static support. The gas struts appear to act as dampers which are set to positions according to occupant movement of an actuating lever. Forward movement of the lever adjust the seat gas strut and rearward movement adjusts the backrest gas strut U.S. Pat. No. 4,521,053 describes a chair in which a backrest part has a front seat portion. These chairs appear to do little to respond to the posture of the occupant and both require adjustment to suit the particular occupant.
PCT patent specification No. WO87/06810 (Savo) describes a chair in which the seat and the backrest are curved where they join and they overlap each other so that their pivot axes are through an imaginary axis of the hip joint of the occupant. While this approach is undoubtedly an improvement because it takes into account the anatomy of the occupant, it appears that the mechanism would be relatively complex to manufacture because of the need for the backrest and the seat to overlap each other and rotate without the benefit of a conventional pivotal joint. Also, this chair does not appear to provide comprehensive support of the torso and legs for different postures.
In general, a major problem with chairs is that they require the occupant to actively and consciously control the chair using actuators to achieve a supportive and comfortable configuration of the chair. An example is the adjustment of a strong spring at the front of a chair to set a required pressure according to the weight of the occupant. Further, the configuration which is reached is either static or provides synchronised seat and backrest tilting. If static, RSI may be a problem. If synchronised, the chair effectively imposes a range of seat/backrest configurations irrespective of the natural posture of the occupant.
It is therefore an object of the invention, to provide a chair which actively provides comprehensive support and promotes and induces joint movement of the user at all times ( is xe2x80x9cposture-responsivexe2x80x9d), while the role played by the occupant is passive (there is no need for actuators or for the occupant to become actively involved in any way).
Another object is to provide a chair having a very simple and robust construction.
According to the invention, there is provided a chair comprising a seat, a backrest, and a fixed support, wherein the seat and the backrest are independently pivotable and are biassed to provide posture-responsive support of an occupant.
In one embodiment, the seat is biassed upwardly at the front and the backrest is biassed forwardly whereby the bias forces are contra-rotational about an occupant""s centre of gravity.
In one embodiment, the backrest bias is transferred to the seat by abutment of the backrest with the seat at some relative positions of the seat and the backrest.
In one embodiment, the seat and the backrest are pivotally mounted on the fixed support.
In one embodiment, the seat is biassed upwardly at the front by a spring acting between the fixed support and the seat forwardly of the seat pivot axis, and the backrest is biassed forwardly by a spring acting between the fixed support and the backrest rearwardly of the backrest pivot axis.
In another embodiment, the fixed support comprises a stop means which sets extremities of independent movement of the seat.
In one embodiment, the fixed support comprises a stop means which sets a rearward extremity of movement of the backrest, and a forward extremity of the backrest is set by abutment with the seat.
In one embodiment, the seat and the backrest are pivotally mounted and the pivot axes are located substantially in the same vertical plane as the centre of gravity of an occupant sitting on the chair.
In a further embodiment, the seat and the backrest pivot axes are coincident.
Preferably, the pivot axes extend through the fixed support.
In one embodiment, the backrest and seat pivot axes comprise a pivot pin extending through the fixed support.
In one embodiment, the backrest comprises a pair of lateral supports interconnected by a pivot joint extending through the fixed support.
In one embodiment, the backrest further comprises a cross-member interconnecting the lateral supports rearwardly of the pivot joint.
In one embodiment, the cross-member is acted upon by a bias means urging the backrest forwardly.
In another embodiment, the fixed support is of U-shaped channel construction and the seat comprises a seat support nested within the fixed support.
In one embodiment, the seat support is of inverted U-shaped channel construction.
In one embodiment, the backrest is biassed forwardly by at least two springs, whereby all springs act at a rearward extremity of the backrest and at least one spring ceases to act as the backrest moves forward.
In one embodiment, the chair further comprises a safety mechanism comprising means for preventing tilting of the seat downwardly at the front if the occupant is sitting at the front edge of the seat.
According to another embodiment, the invention provides a chair mechanism comprising:
fixed support, a seat support comprising means for supporting a seat pad, and a backrest support comprising means for supporting a backrest pad, wherein the seat support and the backrest support are independently pivotable and are biassed to provide posture-responsive support of an occupant of a chair as defined above.